HIGH-SENSITIVITY DETECTION OF 4-(3-PYRIDINYLMETHYLAMINOCARBOXYPROPYL)PHENYLTHIOHYDANTOINS BY CAPILLARY LIQUID-CHROMATOGRAPHY MICROELECTROSPRAY ION-TRAP MASS-SPECTROMETRY

We describe the separation and detection at the low-femtomole level of 4-(3-pyridinylmethylaminocarboxypropyl) phenylthiohydantoins (311-PTH s) by capillary liquid chromatography-microelectrospray ion trap mass spectrometry. Highest sensitivity was obtained in the multiple-ion mon itoring operating mode in which we detected 311-PTHs at the 5-fmol lev el with a signal-to-noise ratio of approximately 10. We investigated t he fragmentation patterns of the isobaric 311-PTH isoleucine and 311-P TH leucine by electrospray ionization ion trap tandem mass spectrometr y. The compounds could be differentiated by a fragment ion of mass m/z = 366.1 which was specific for the breakdown of 311-PTH leucine, thus allowing for the unambiguous identification of the 311-PTH derivative s of all 20 naturally occurring amino acids by their masses and fragme ntation patterns.